import math
x1,y1,x2,y2 = map(float,raw_input().split(' '))
x = abs(x1-x2);
y = abs(y1-y2);
a = math.sqrt(x**2 + y**2) 
print a import math math x1,y1,x2,y2 = map(float,raw_input().split(' ')) x1 map(float,raw_input().split(' ')) map float raw_input().split(' ') ().split () raw_input split ' ' y1 x2 y2 x = abs(x1-x2) x abs(x1-x2) abs x1-x2 x1 x2 y = abs(y1-y2) y abs(y1-y2) abs y1-y2 y1 y2 a = math.sqrt(x**2 + y**2) a math.sqrt(x**2 + y**2) math.sqrt math sqrt x**2 + y**2 x**2 x 2 y**2 y 2 print y1,x2,y2 = map(float,raw_input().split(' ')) map(float,raw_input().split(' ')) y1 x1,y1,x2,y2 = map(float,raw_input().split(' ')) map(float,raw_input().split(' ')) x1 y2 = map(float,raw_input().split(' ')) map(float,raw_input().split(' ')) y2 a = math.sqrt(x**2 + y**2) math.sqrt(x**2 + y**2) a y = abs(y1-y2) abs(y1-y2) y x2,y2 = map(float,raw_input().split(' ')) map(float,raw_input().split(' ')) x2 x = abs(x1-x2) abs(x1-x2) x
import math
x1,y1,x2,y2 = map(float,raw_input().split(' '))
x = abs(x1-x2);
y = abs(y1-y2);
a = math.sqrt(x**2 + y**2) 
print a